Stellar uncertainty: what we don’t know about the sun

A perspective in this week's edition of Science describes how we can't get our …

Despite being pretty obvious, the sun is remarkably obscure. That's the conclusion of a perspective that describes our current understanding of that essential body that appeared in Science yesterday. The paper provides a nice description of why the people studying the sun can't agree, what they're doing to change that, and why the whole topic is actually pretty important for lots of other fields.

The sun has such broad emissions and absorption lines that it can be hard to tell its precise elemental composition; imaging results have to be fed into models that include information on the circulation of matter and energy in order to generate estimates of its elemental composition. In the past, these models had to simplify the circulation, but they produced estimates that were in line with data obtained about the body's interior.

The unfortunate bit about these estimates is that they indicated that the sun had far more heavy elements than the local interstellar medium that it ostensibly formed from. In recent years, scientists have replaced their surface models with more sophisticated, three-dimensional circulation models, and these have produced results that suggest a much lower concentration of heavy elements, bringing the sun back in line with the interstellar medium. The downside of this data is that it broke something rather important: its agreement with what we think is going on inside the sun.

If the surface composition is used to construct a model of the interior, it produces something that's inconsistent with the data obtained from helioseismology, which tracks the propagation of sound waves through the interior of the sun. The perspective mentions a few different avenues by which researchers have tried to bring the two approaches back in line, but notes that the most promising ones have already failed. The whole problem is magnified by the fact that, as the most conveniently located object to study, the sun informs our understanding of stellar evolution in general. Getting it wrong here has implications for a lot of other systems astronomers care about.

There may yet be a way to bring everything into line, but it's important to emphasize a couple of aspects of this problem. The first is that, even in those cases where your average person will think science has things sorted out, the controversies over the details can be pretty substantial. The second is that the controversial bits doesn't mean our general understanding—in this case, fusion fueled by gravitational collapse—is all wrong. As other areas of science sporadically erupt into public controversy, these two aspects of the endeavor could be emphasized a bit more.